Direct-Metal Bonded (DMB) substrates (also called Direct Bonded Metal (DBM) substrates are used extensively in the power semiconductor industry. DMB substrates include Direct Copper Bonded (DCB) substrates (also called Direct-Bonded Copper (DBC) substrates) and Direct Aluminum Bonded (DAB) substrates (also called Direct-Bonded Aluminum (DBA) substrates.
In the case of the metal being copper, a DCB substrate generally includes a ceramic sheet substrate member, to which a thinner top plate of copper and a thinner bottom plate of copper are bonded. After direct bonding of the copper plates to the ceramic substrate member, the copper plates are patterned and etched so that islands of desired shapes are formed out of the copper on the top and bottom of the panel. The copper is then typically plated with nickel or some other plating metal. The resulting DCB panel is then cut into smaller individual DCB substrates. One or more semiconductor dice are generally surface mount attached to the top metal of a DCB substrate, and the DCB substrate/die assembly is incorporated into a semiconductor device package to form a final packaged semiconductor device.
There are numerous methods for making DCB substrates. A typical ceramic panel is about 150 millimeters wide by 200 millimeters long and about half a millimeter thick. Such a ceramic panel is made to rest on a U-shaped carrier. A thin plate of thinly oxidized copper metal is placed on top of the ceramic panel. The assemblage is placed in a furnace such that the copper plate bonds to the ceramic panel. The bonded structure is removed from the furnace, is allowed to cool at least somewhat, and is flipped over, and is put back onto the U-shaped carrier. A second thin plate of slightly oxidized copper is placed on the ceramic panel. The assemblage is placed back into the furnace and is heated up again such that the second plate of metal is bonded to the ceramic. In this way, a first sheet of copper is direct-bonded to a top surface of the ceramic panel and a second sheet of copper is direct-bonded to a bottom surface of the ceramic panel. There is a first heating step, then a first cooling, then a second heating step, then a second cooling. Such multiple heating and cooling steps can cause problems including bending and warping of the final DCB panel. The final DCB panel is patterned, plated, and cut into individual DCB substrates.
Another method for making a DCB substrate is set forth in U.S. Pat. No. 8,377,240. Advantageously, the method allows both copper plates to be direct-bonded to a central ceramic panel in a single heating step. A powder of a temperature resistant material is baked or otherwise bonded together to form a so-called separating layer. One such separating layer structure is disposed on each raised area of a carrier. A DCB panel stack involving a slightly oxidized bottom copper plate, a ceramic panel, and a slightly oxidized top copper plate is placed onto the carrier. The carrier with the DCB panel stack resting on it is then placed into a furnace. The copper plates are direct-bonded to the ceramic panel in a single high temperature heating step. In the direct-bonding process, ceramic particles from the separating layer adhere to the bottom metal plate. These ceramic particles are then removed by brushing and/or chemical etching. The resulting DCB panel is then patterned, plated, and cut into individual DCB substrates.
Additional methods for making DCB substrates are set forth in U.S. Pat. No. 8,876,996. In one method, a special ceramic carrier is used. The ceramic carrier has rows of upward facing pyramid-shaped projections. The tips of these pyramid-shaped projections are flat to form very small contact surfaces. A DCB panel stack involving a slightly oxidized bottom copper plate, a ceramic panel, and a slightly oxidized top copper plate is placed to rest on the contact surfaces of the pyramid-shaped projections of the carrier. The assemblage is heated so that the top and bottom copper plates are direct-bonded to the ceramic panel in a single heating step. As explained in U.S. Pat. No. 8,876,996, the carrier offers the advantage of there being no need for an additional separating layer. The patent teaches that due to the special structuring of the carrier, with the very small contact points, the bonded DCB assemblage can be detached from the carrier after the bond process, free of any residue. The resulting DCB panel is patterned, nickel plated, and cut into individual DCB substrates.
DCB substrates have been made commercially and successfully with these methods and techniques for many years.